Evolution under exposure to heatwaves in the seed beetle, Callosobruchus maculatus.

Heatwave increases in frequency, intensity, and duration, are arguably the most straightforward manifestations of anthropogenic global warming and have devastating impacts on many ecosystems and taxa. However, to date, most studies investigating these impacts have focused on populations that have evolved under constant conditions prior to assaying or have only investigated the short-term outcomes. Here, using the seed beetle, Callosobruchus maculatus, we investigated both the short- and long-term effects of evolution after 43 generations of daily fluctuating temperature with an added heatwave exposure (+2°C peaking at 42°C) on two important life history traits, development time and lifetime reproductive success (LRS). We find that populations evolved under heatwave exposure developed at similar rates but had lower LRS than those evolved and assayed under the same fluctuating conditions. When assayed at a novel benign temperature of 29°C, beetles from both thermal regimes developed slower but had similar LRS, which was significantly higher than when assayed under the stressful fluctuating environment. Together, this suggests that long-term heatwave exposure may increase resilience to both repeated heatwaves and sudden environmental changes. This study emphasises the potency of long-term multigenerational exposure to heatwaves in order to understand how populations respond to climate change.